This invention relates generally to thrust bearings, and more particularly to sealed anti-friction thrust bearings. By way of example but not of limitation, bearings of said type are used in automobiles as clutch release or clutch throw-out bearings.
Generally speaking, automotive clutch throw-out bearings are well-known in the art. Their function is to provide a force transmitting member between the foot-operated clutch pedal and a plurality of rotating clutch release arms associated with the pressure plate on an automotive clutch. These clutch throw-out bearings are subjected to substantial forces over long periods of use and are consequently required to be of superior strength and durability to prevent premature failure. Moreover, these bearings are used in large quantities, and large scale manufacturing techniques are incorporated so as to minimize their cost to the automotive manufacturers. Typical such clutch throw-out bearings are disclosed and claimed, for example, in U.S. Pat. Nos. 3,909,086 and 4,046,436.
One important consideration in the design of such bearings is that of maintaining adequate amounts of lubricant over the relatively moving surfaces of the bearing. More particularly, it is important that the balls or other bearing elements retain a proper amount of grease or other lubricating material. In this regard, several characteristics in the operation of conventional thrust bearings tend to discourage rather than encourage such retention of lubricant. For example, in operation the rotation of the relatively rotatable parts of the bearing tend to generate heat which in turn encourages "bleed-down" of the grease or other lubricant which then comes into contact with the rotating surfaces and is thrown outwardly of the rotating surfaces. This outwardly thrown grease or other lubricant then tends to be caught upon the interior surface of the bearing shell, rather than on the balls or other bearing elements.
A second characteristic of many prior art thrust bearings is the tendency to experience "drop down" while in service. Briefly, by this it is meant that a normal amount of play or tolerance is conventionally encountered between the raceways provided for the balls or other bearing elements. This play allows some movement of the bearing elements away from their intended seating in the raceways so as to result in an accelerated rate of wear of these parts. In other words, the balls or other bearing elements tend to move somewhat out of the provided raceways and wear at their edges, sometimes resulting in premature failure of the bearing.